They were in my range bag and the plastic bag kept the same mags and maglua and empty chamber indicator together. Never got wet, but hadn't used them for several months so I didn't notice. If I had oiled them probably no problem, but I bet the plastic bag didn't help. The bag was not sealed or anything. The range bag was in the garage.For the OP, why the plastic bags?
I haven't tried it myself, but several people have recommended car wax to prevent corrosion. Seems like it might be worth a try.
BTW, the only one of my magazines that ever rusted was in a plastic bag. Experiment complete, lesson learned!
I have a couple of those Sneaky Pete Ammo Armor sleeves, for my pocket mags. On and off real easy, andkeeps them from getting clogged with lint and stray Skittles. Keeps the fingerprints off the mags, too.For the moment, the advice to remove the surface rust should put you back in business. Yeah, the bags, and temperature change, are likely culprits.
BTW, Sneaky Pete now markets those plastic mag covers that let you pocket a spare mag; protects from lint and pocket junk. But it wouldn't hurt to give the mags a wipe with a silicone rag.
We've all gotten a little sloppy with the advent of stainless or other rust resistant gun finishes. My blued safe queens get wiped after a handling, but the carry stuff gets an as needed cleaning.
Fortunately, SIG mags aren't hard to detail strip, so there's no drama in cleaning/wiping the inside as well.
It happens. One night last Fall I forgot I hadn't removed my backup mag and its carrier from my jeans and washed both as well as the SD ammo in the magazine. I realized what I'd done when I heard the dryer going "thunk, pause, pause, thunk, pause, thunk" etc. Immediately fished it out of the dryer, removed it from the mag holder, unloaded it, inspected the rounds, set them aside, took the magazine apart, dried it with a microfiber towel, CLPed the inside, outside, spring, and baseplate using the SLIP2000 EWL 30 I linked to above, let it sit for five minutes, gave it a wipe with a different microfiber towel, applied one more light coat, let that sit for five more minutes, gave it a wipe with the microfiber towel, and done. The SD ammo was set aside to use only at the range for practice and fresh ammo was reloaded into the magazine.They were in my range bag and the plastic bag kept the same mags and maglua and empty chamber indicator together. Never got wet, but hadn't used them for several months so I didn't notice. If I had oiled them probably no problem, but I bet the plastic bag didn't help. The bag was not sealed or anything. The range bag was in the garage.
edit: The mags I pocket carry don't have a problem.
edit2: I might have closed the bag after all, don't remember.